Torsion suspensions (a.k.a, torsion spring suspensions, torsion bar suspensions, etc.) are commonly used in vehicles such as trailers. Torsion suspensions are relatively simple, lightweight and cost efficient and are hence well suited to be used in some trailers towed by vehicles. A torsion suspension unit typically comprises a housing by which the torsion suspension unit is secured to the trailer. A shaft (a.k.a., a torsion bar) has a portion within the housing and another portion projecting out of the housing. The wheels of the vehicle are connected to an arm that is integrally connected to the shaft, the arm (a.k.a., lever) being at a right angle relative to the shaft (or quasi right angle). The portion of the shaft that is in the housing is received in a body of rubber or like resilient material. The shaft and the rubber are bonded or operatively connected, such that a rotation of the shaft will cause deformation of the rubber, which in turn produces torsion forces on the shaft. The rubber will want to return to its rest state, thereby biasing the shaft toward that position. The torsion effect of the rubber on the shaft is a damped oscillation, leading the shaft to reach an equilibrium state.
One issue related to the use of such torsion suspensions is that the systems rely on the elasticity of the rubber to perform the act of suspension. If a trailer is for instance overloaded, the rubber may be ineffective in damping the oscillations and returning the trailer to an equilibrium state.